1. Field of the Invention
This invention relates to server apparatuses, server control programs, and client apparatuses in a computer system configured to cause all of the applications input and output at a client personal computer (PC) to run on a server in a client-server system connected via a network, such as a local area network (LAN).
2. Description of the Related Art
Each of the individual PC terminals connected to a network, such as an in-house LAN, has run a document creation application or a spreadsheet application independently and created various files. The various files have been stored in the storage unit of the PC terminal or in an external storage medium, such as a magnetic disk, an optical disk, or a small semiconductor memory, or have been transferred to and stored in a storage unit managed by a server on the network.
In such a conventional client-server system, since the created files are managed in each PC terminal itself, if the PC terminal has been lost or carried out illegally and fallen into the third party's hands, there is a risk that the stored files might be read out and important information or classified information might be leaked.
Moreover, when each PC terminal runs the application independently, the work of updating, changing, and adding the application has to be done on a PC terminal basis, making management troublesome, which results in an increase in the cost.
To overcome this drawback, a recent client-server system has introduced a server-based computing (SBC) system [thin client system] configured to run all the applications input and output at each PC terminal (or client PC) on the server and manage all the created files on the server side (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-171063 and Jpn. Pat. Appln. KOKAI Publication No. 2003-158534).
In such a thin client system, the drawing data of the application executed on the server side is transferred to the client PC, which then displays the drawing data (for example, Jpn. Pat. Appln. KOHYO Publication No. 2004-503862).
As described above, in the thin client system, drawing data for the application software program executed on the server side is transferred to the client PC. The drawing data is displayed on the client PC. Therefore, when the amount of drawing data to be processed increases or when the number of client PCs connected to the server increases, the server's burden of transferring the drawing data to the client increases. This causes the following problems: the response speed between the server and the client drops and the number of client PCs to be connected has to be limited drastically.
To overcome the problems, a method of alleviating the processing burden due to the transfer of drawing data by clipping only a rectangular drawing area including the drawing data part updated on one screen and transferring and rewriting the drawing area has been considered as the technique for controlling the display of drawing data by software. However, as the resolution of drawing data has been getting higher and the monitor resolution has improved spectacularly, the amount of data to be processed for the drawing has increased further and therefore the processing burden is required to be alleviated more.